SAVEcho-planar imaging (EPI) allows a magnetic resonance image to be acquired in less than 0.1 sec, which is orders of magnitude faster than existing MR modalities. This fast imaging technique allows us to monitor biological processes that evolve rapidly in time without observable motion artifacts, such as thermal conduction and molecular diffusion. We are extending the work of Dr. Robert Turner (formerly with the BEIP, NCRR, and now with the Laboratory of Cardiac Energetics, NHLBI) to develop this EPI diffusion system on the 4.7-T MRI system at the In Vivo NMR Research Center. Moreover, to account for the complex interactions between imaging and diffusion gradients applied in typical diffusion-weighted imaging pulse sequences, we have derived analytic expressions for "b-matrix" elements needed to estimate the effective self-diffusion tensor off-line.